Phosphor layer arrangement for use with light emitting diodes

ABSTRACT

Phosphor layer arrangement for use with light emitting diodes. In an aspect, a light emitting diode apparatus is provided that includes a least one light emitting diode, an encapsulation covering the at least one light emitting diode, a lens having a phosphor layer formed upon a bottom surface, the lens positioned to cover at least part of the encapsulation, and an air gap between the phosphor layer and the encapsulation. In an aspect, a light emitting diode lamp is provided that includes a package, a least one light emitting diode, an encapsulation covering the at least one light emitting diode, a lens having a phosphor layer formed upon a bottom surface, wherein the lens is positioned to cover at least part of the encapsulation, and an air gap between the phosphor layer and the encapsulation.

RELATED APPLICATIONS

This patent application is a Divisional patent application of patentapplication Ser. No. 12/208,142, filed on Sep. 10, 2008 entitledPHOSPHOR LAYER ARRANGEMENT FOR USE WITH LIGHT EMITTING DIODES, theentire content of which is hereby expressly incorporated by reference.

BACKGROUND

The present application relates generally to light emitting diodes, andmore particularly, to a phosphor layer arrangement for use with lightemitting diodes to provide enhanced light output.

Light emitting diodes (LEDs) for use as indicators are well known. LEDshave been used extensively for this purpose in consumer electronics. Forexample, red LEDs are commonly used to indicate that power has beenapplied to devices such as radios, televisions, video recorder (VCRs)and the like.

Recently, high-power LEDs have seen increased use in general lightingapplications. For example, high-power LEDs can now be found in overheadlighting, street lighting, and in automotive application, such as inautomobile headlamps. Typically, high-power LEDs are provided as anassembly comprising one or more LEDs mounted to a substrate andprotected by an encapsulation. Light emitted from the LEDs passesthrough and is focused by the encapsulation before it is visible to auser.

It is desirable to have high-power LED assemblies that produce light ofdifferent colors. For example, white light can be produced by usingphosphor to convert blue light emitted from an LED. In conventional LEDassemblies, an organic phosphor dye is use to coat the LED chip.Unfortunately, this arrangement has poor conversion efficiency and lowlight output because of “backscatter.” Backscatter occurs because thephosphor layer is in direct contact with the LED chip causing light toreflect back toward the LED chip thereby decreasing light output.

Therefore, what is needed is a way to avoid the problems associated withbackscatter to increase the optical output of high power LEDs

SUMMARY

In one or more aspects, a phosphor layer arrangement is provided for usewith one or more light emitting diodes to overcome the problemsassociated with backscatter to provide increased optical output.

In an aspect, a light emitting diode apparatus is provided thatcomprises a least one light emitting diode, an encapsulation coveringthe at least one light emitting diode, a lens having a phosphor layerformed upon a bottom surface, the lens positioned to cover at least partof the encapsulation, and an air gap between the phosphor layer and theencapsulation.

In an aspect, a method is provided for forming a light emitting diodeapparatus. The method comprises encapsulating at least one lightemitting diode with an encapsulation, covering the encapsulation with alens having a phosphor layer formed upon a bottom surface, wherein anair gap is formed between the encapsulation and the phosphor layer.

In an aspect, a light emitting diode lamp is provided that comprises apackage, a least one light emitting diode, an encapsulation covering theat least one light emitting diode, a lens having a phosphor layer formedupon a bottom surface, wherein the lens is positioned to cover at leastpart of the encapsulation, and an air gap between the phosphor layer andthe encapsulation.

In an aspect, an illumination device is provided that comprises a powersource and a light emitting diode lamp in electrical communication withthe power source. The light emitting diode lamp comprises a package, aleast one light emitting diode, an encapsulation covering the at leastone light emitting diode, a lens having a phosphor layer formed upon abottom surface, wherein the lens is positioned to cover at least part ofthe encapsulation, and an air gap between the phosphor layer and theencapsulation.

In an aspect, a light emitting diode apparatus is provide that comprisesa least one light emitting diode, an encapsulation covering the at leastone light emitting diode, and a lens having a phosphor layer formedbetween first and second lens portions, the lens positioned so that thesecond lens portion fits against the encapsulation.

Other aspects will become apparent after review of the hereinafter setforth Brief Description of the Drawings, Description, and the Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects described herein will become more readily apparentby reference to the following Description when taken in conjunction withthe accompanying drawings wherein:

FIG. 1 shows an exemplary substrate for use with aspects of a phosphorlayer arrangement;

FIG. 2 shows the substrate of FIG. 1 with a silicone encapsulation foruse in aspects of a phosphor layer arrangement;

FIG. 3 shows exemplary side and bottom views of a lens for use inaspects of a phosphor layer arrangement;

FIG. 4 shows an exemplary LED assembly having aspects of a phosphorlayer arrangement;

FIG. 5 shows a detailed view of an exemplary stepped reflector for usein aspects of a phosphor layer arrangement;

FIG. 6 shows an exemplary lens for use in aspects of a phosphor layerarrangement;

FIG. 7 shows an exemplary LED assembly having aspects of a phosphorlayer arrangement;

FIG. 8 shows an exemplary method for providing LED assembles havingaspects of a phosphor layer arrangement; and

FIG. 9 shows exemplary devices suitable for use with LED assembliesconfigured to have aspects of a phosphor layer arrangement.

DESCRIPTION

In various aspects, a phosphor layer arrangement is provided for usewith one or more light emitting diodes so as to provide increasedoptical output.

FIG. 1 shows an exemplary substrate 100 for use with aspects of aphosphor layer arrangement. The substrate 100 comprises three LED diesshown generally at 102 that are mounted to substrate material 104.Although three LED dies are shown, aspects of the phosphor layerarrangement are suitable for use with any number of LED dies. In anaspect, the substrate material 104 comprises at least one of Al, Cu,AlN, and AlSiC. However, the substrate material 104 may comprise of anysuitable material. The LED dies 102 are mounted to the substratematerial 104 with a thermal interface material 106. A plastic lamination108 is also mounted to the substrate material 104. The plastic (or FR4)lamination 108 comprises a lead frame 110 sandwiched between upper 112and lower 114 layers of plastic (or FR4). The lead frame 110 comprisescopper or silver and allows power to be routed to the LED dies 102. Theplastic (or FR4) lamination 108 and substrate 104 include a slot 116 toallow for mounting of a lens which is described in detail in anothersection of this document.

Silver plate reflectors 118 are mounted on the plastic (or FR4)lamination 108 to form a stepped reflector which exposes a portion ofthe lead frame 110 to provide a bonding region to attach to a bondingwire 120. A more detailed description of the stepped reflector region122 is provided in another section of this document

FIG. 2 shows the substrate 100 with a silicone encapsulation 202 for usein aspects of a phosphor layer arrangement. For example, theencapsulation 202 is molded or otherwise formed within the regionbounded by the stepped reflector 204. The encapsulation 202 operates toprotect the LED dies 102 and bonding wires 120. The encapsulation 202also operates to extract light emitted from the LED dies 102.

FIG. 3 shows side and bottom views of an exemplary lens 300 for use inaspects of a phosphor layer arrangement. The lens 300 is configured tofocus light emitted by the LED dies 102 and extracted by theencapsulation 202. The lens 300 includes a domed focusing portion 302that comprises glass or plastic and is configured to fit over theencapsulation 202. The lens 300 also comprises a ridge feature 304 thatis configured to fit into the slot 116 shown in FIG. 1. As illustratedat 308, there is a break in the ridge feature to provide a path for thelead frame 110.

A phosphor layer 306 is formed upon a bottom surface of the lens 300. Invarious aspects, the phosphor layer 306 may be deposited, etched,attached, or otherwise prepared or fabricated upon the bottom surface ofthe lens 300. For example, the phosphor layer is coated or molded ontothe bottom surface of the lens 300 with a thickness that depends on theoptical design to produce the maximum light output (i.e., lumens perwatt). It should be noted that aspects of the phosphor layer arrangementare not limited to producing only white light because different type ofphosphor may be used to produce a different color light.

The phosphor layer 306 is configured to efficiently convert blue lightemitted from the LED dies 102 into white light. In an aspect, thephosphor layer 306 comprises an inorganic dye distributed with a uniformthickness over the bottom surface of the lens 300. In another aspect,the phosphor layer 306 is distributed with varying thicknesses over thebottom surface of the lens 300. For example, in an aspect, the phosphorlayer 306 is distributed with a thickness in the range of 5 to 500microns. Thus, the application of the phosphor layer 306 to the bottomsurface of the lens can be done with any desired thickness to achievehighly efficient conversion of light.

FIG. 4 shows an exemplary LED assembly 400 having a phosphor layerarrangement. In the assembly 400, the lens 300 is fitted on thesubstrate material 104 by inserting the ridge feature 304 into the slot116 as illustrated at 402. When the lens 300 is fitted on the substratematerial 104, the phosphor layer 306 is positioned above theencapsulation 202 so that light passing through the encapsulation 202will strike the phosphor layer 306. In an aspect, an adhesive is used toseal the lens 300 into position.

When the lens 300 is in place, an air gap 404 is formed between theencapsulation 202 and the phosphor layer 306. In an aspect, the air gapis in the range of 5 to 1000 microns thick. The air gap 404 provides alower refractive index between the encapsulation 202 and the phosphorlayer 306 that allows more light to pass through the phosphor layer 306and reduces the amount of light reflected back into the encapsulation202 as backscatter. For example, without the phosphor layer arrangementdescribed herein, backscatter may account for 60% of the light emittedfrom the LED dies. With the phosphor layer arrangement described herein,there may be up to a 20-30% improvement in light total output. Thus,more light is output from the lens 300.

The size of the air gap is determined by the shape of the lens 300, theencapsulation 202, and the phosphor layer 306. By controlling thesegeometries, an air gap of virtually any size or shape can be formed soas to reduce backscatter and maximize the amount of light output fromthe lens.

It should also be noted that in various aspects, the geometries and/orshapes described with reference to the phosphor layer 306 and the airgap 404 may have varying dimensions. Thus, in various aspects, aphosphor layer arrangement may be formed have varying dimensions and isnot limited to having the exact features or dimensions described herein.

FIG. 5 shows a detailed view of the stepped reflector region 122illustrated in FIG. 1. The stepped reflector region 122 is formed byreducing the amount of plastic material of the upper plastic layer 112so as to expose a bonding area 502 of the lead frame 110. Reflectivematerial 118 is placed on the upper plastic 112 and lower plastic 114surfaces as illustrated. The reflective material 118 may be Ag or anyother suitable material. A bonding wire 120 can be attached to thebonding area 502 to provide power to the LED die 102. As illustrated,both the upper 112 and lower 114 regions of the stepped reflectorreflect light emitted from the die 102 as shown at 124.

Thus, aspects of a phosphor layer arrangement comprises a steppedreflector that provides a bonding region while providing a reflectiveregion to reflecting light emitted from the LED die 102.

FIG. 6 shows an exemplary lens 600 for use in aspects of a phosphorlayer arrangement. The lens 600 is configured to focus light emitted bythe LED dies 102 and extracted by the encapsulation 202. The lens 600includes a first lens portion 602 that comprises glass or plastic and isconfigured to fit onto the substrate 104. The first lens portion 602also comprises a ridge feature 604 that is configured to fit into theslot 116 shown in FIG. 1. In an aspect, the ridge feature 604 alsoincludes a break (or recess) to provide a path for the lead frame 110.

A phosphor layer 606 is formed upon a bottom surface of the first lensportion 602. In various aspects, the phosphor layer 606 may be disposedon, deposited, etched, attached, or otherwise prepared or fabricatedupon the bottom surface of the first lens portion 602. For example, thephosphor layer is coated or molded onto the bottom surface of the firstlens portion 602 with a thickness that depends on the optical design toproduce the maximum light output (i.e., lumens per watt). It should benoted that aspects of the phosphor layer arrangement are not limited toproducing only white light because different type of phosphor may beused to produce a different color light.

The phosphor layer 606 is configured to efficiently convert blue lightemitted from the LED dies 102 into white light. In an aspect, thephosphor layer 606 comprises an inorganic dye distributed with a uniformthickness over the bottom surface of the first lens portion 602. Inanother aspect, the phosphor layer 606 is distributed with varyingthicknesses over the bottom surface of the first lens portion 600. Forexample, in an aspect, the phosphor layer 606 is distributed with athickness in the range of 5 to 500 microns. Thus, the application of thephosphor layer 606 to the bottom surface of the lens can be done withany desired thickness to achieve high efficiency conversion of light.

The lens 600 also comprises a second lens portion 608 that comprisesglass or plastic having a low refractive index. In an aspect, the secondlens portion 608 may be any suitable transparent material with a lowindex of refraction. Transparent means no significant obstruction orabsorption of electromagnetic radiation in the particular wavelength (orwavelengths) of interest.

The second lens portion 608 adheres to the phosphor layer and has ashape and thickness based on the following factors:

-   1. Phosphor layer shape and thickness-   2. Encapsulation shape-   3. Contoured to provide a small air gap or no air gap between the    second lens portion 608 and encapsulation.

Thus, because of the low refractive index of the second lens portion608, less backscatter will occur and more light will be focused to passthrough the phosphor layer 606 and be converted to white light. Itshould also be noted that in another aspect, the phosphor layer 606 isformed upon a top surface of the second lens portion 608. Thus, severaltechniques are possible to generate a phosphor layer arrangement wherethe phosphor layer 606 is formed between the first and second lensportions.

FIG. 7 shows an exemplary LED assembly 700 having aspects of a phosphorlayer arrangement. In the assembly 700, the lens 600 is fitted onto thesubstrate material 702 by inserting the ridge feature 604 into a slotformed in the substrate material as illustrated at 702. When the lens700 is fitted on the substrate material 702, the phosphor layer 606 ispositioned above the encapsulation 704. In an aspect, an adhesive isused to seal the lens 600 into position.

When the lens 600 is in place, the second lens portion 608 fits againstthe encapsulation 704 with little or no air gap. The second lens portion608 provides a low refractive index between the encapsulation 704 andthe phosphor layer 606 that reduces backscattering and allows more lightto pass through the phosphor layer 606. Thus, the amount of lightreflected back into the encapsulation 704 as backscatter is reduced andmore light is output from the lens 600.

It should also be noted that in various aspects, the geometries orshapes described with reference to the lens 600 and the phosphor layer606 may have varying dimensions. Thus, aspects of a phosphor layerarrangement may have varying dimensions and are not limited to havingthe exact features or dimensions described herein.

Formation of a Phosphor Layer Arrangement

FIG. 8 shows an exemplary method 800 for providing LED assembles havingaspects of a phosphor layer arrangement. For clarity, the method 800 isdescribed below with reference to the phosphor layer arrangement shownin FIG. 4 and FIG. 7.

At block 802, a substrate is configured. For example, the substrate isconfigured to carry one or more LED dies and to have a slot, such asslot 116 shown in FIG. 1, for mounting a lens. In an aspect, thesubstrate is comprised of Al, Cu, AlN, AlSiC or other suitable material.

At block 804, a plastic lamination having a stepped reflector is mountedto the substrate. The plastic (or FR4) lamination includes a lead framecomprising Cu and/or Ag to provide power to the LED dies. The steppedreflector is configured to expose a bonding pad on the lead frame whileproviding reflecting surfaces to reflect light emitted from the LEDdies. For example, the reflecting surfaces comprise Ag plate reflectors.

At block 806, one or more LED dies are attached to the substrate using athermal interface material. In an aspect, the LED dies emit blue lightwhen power is applied.

At block 808, the LED dies are wire bonded to the lead frame. Forexample, the LED dies are wire bonded to the bonding pads of the leadframe that are exposed by the stepped reflector of the plasticlamination. The lead frame carries power to the LED dies via the bondedwires.

At block 810, a silicone encapsulation is dispensed within the regionformed by the stepped reflector and the substrate to cover the LED diesand bonding wires. The encapsulation operates to extract light and maycomprise any suitable shape, such as a domed shape.

At this point, one of two phosphor layer configurations may be formed. Afirst configuration is formed by blocks 812 through 816. A secondconfiguration is formed by blocks 818 through 824.

First Phosphor Layer Arrangement Configuration

At block 812, a lens is configured. In an aspect, the lens operates tofocus light from the LED dies and is configured to have a domed shape.The lens also has a ridge features (i.e., ridge feature 304 asillustrated in FIG. 2, for mounting to the substrate.

At block 814, a phosphor layer is formed upon a lens surface. Thephosphor layer converts the blue light emitted from the LED dies towhite light. In an aspect, the phosphor layer is an inorganic dye thatis molded on a bottom surface of the lens and may be uniform ornon-uniform in thickness. In an aspect, the phosphor layer may beconfigured to have any desired shape and/or thickness.

At block 816, the lens is attached to the substrate to provide aphosphor layer arrangement with an air gap. In an aspect, the lens isfitted over the encapsulation and is mounted to the substrate byinserting the ridge features of the lens into the slots of thesubstrate. Any type of glue or adhesive may be used to secure the lensto the substrate. In an aspect, the lens is configured so that an airgap is formed between the encapsulation and the phosphor layer. The airgap may be configured to have any desired thickness and/or shape. In anaspect, the air gap provides a low refractive index that reducesbackscatter to allow light emitted from the LED dies to pass through thephosphor layer.

Second Phosphor Layer Arrangement Configuration

At block 818, first and second lenses are configured. For example, thefirst and second lenses are configured to fit together and to mount onthe substrate. The first and the second lens are configured to focuslight emitted from the LED dies. The first and second lens may have anysuitable shape, and when they are fit together they define an internalregion with pre-determined dimensions.

At block 820, a phosphor layer is formed upon a lens surface. In anaspect, an inorganic phosphor dye is formed upon the bottom surface ofthe first lens or on the top surface of the second lens. Thus, thephosphor layer is formed between the first and second lenses. Thephosphor layer is configured to have any desired thickness and fitwithin the internal region defined by the two lens portions.

At block 822, the first and second lenses are attached together to forma lens assembly. In an aspect, the lenses are attached by the adhesionof the phosphor layer.

At block 824, the lens assembly is attached to the substrate to form aphosphor layer arrangement. In an aspect, the lens assembly is mountedto the substrate material using a ridge feature and is sealed onto thesubstrate material with adhesive. When the lens assembly is mounted ontothe substrate material, either no air gap or a small air gap is formedbetween the encapsulation 202 and the lens assembly. The second lensportion provides a low refractive index that reduces backscatter toallow more light to pass through the phosphor layer.

Therefore, the method 800 operates to provide a LED assembly comprisingaspects of a phosphor layer arrangement as described herein. It shouldbe noted that the operations of the method 800 may be rearranged orotherwise modified within the scope of the various aspects. Thus, otherimplementations are possible with the scope of the various aspectsdescribed herein.

FIG. 9 shows exemplary devices 900 suitable for use with LED assembliescomprising aspects of a phosphor layer arrangement as described herein.FIG. 9 shows a lamp 902, an illumination device 904, and a street light906. Each of the devices shown in FIG. 9 includes a LED assembly havinga phosphor layer arrangement, to provide efficient conversion andextraction of white light. For example, the lamp 902 comprises a package916 and a LED assembly 908 that includes one or more LEDs and a phosphorlayer arrangement to convert and extract light. The lamp 902 may be usedfor any type of general illumination. For example, the lamp 902 may beused in an automobile headlamp, street light, overhead light, or in anyother general illumination application. The illumination device 904comprises a power source 910 that is electrically coupled to a lamp 912,which may be configured as the lamp 902. In an aspect, the power source910 may be batteries or any other suitable type of power source, such asa solar cell. The street light 906 comprises a power source connected toa lamp 914, which may be configured as the lamp 902. In an aspect, thelamp 914 comprises a LED assembly that includes one or more LEDs and aphosphor layer arrangement to convert and extract light

It should be noted that aspects of the phosphor layer arrangementdescribed herein are suitable for use with virtually any type of LEDassembly, which in turn may be used in any type of illumination deviceand are not limited to the devices shown in FIG. 9. Thus, the phosphorlayer arrangement described herein provides for efficient conversion andincreased extraction of light emitted from one or more LEDs and can beused in a variety of device applications.

The description of the disclosed aspects is provided to enable anyperson skilled in the art to make or use the present invention. Variousmodifications to these aspects may be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects, without departing from the spirit or scope of theinvention. Thus, the present invention is not intended to be limited tothe aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein. Theword “exemplary” is used exclusively herein to mean “serving as anexample, instance, or illustration.” Any aspect described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects.

Accordingly, while aspects of a phosphor layer arrangement have beenillustrated and described herein, it will be appreciated that variouschanges can be made to the aspects without departing from their spiritor essential characteristics. Therefore, the disclosures anddescriptions herein are intended to be illustrative, but not limiting,of the scope of the invention, which is set forth in the followingclaims.

1. A light emitting diode lamp comprising: a package; a least one lightemitting diode; an encapsulation covering the at least one lightemitting diode; a lens having a phosphor layer formed upon a bottomsurface, wherein the lens is positioned to cover at least part of theencapsulation; and an air gap between the phosphor layer and theencapsulation.
 2. The lamp of claim 1, wherein said phosphor layercomprises an inorganic dye.
 3. The lamp of claim 1, wherein saidphosphor layer has a uniform thickness.
 4. The lamp of claim 1, whereinsaid phosphor layer has a varying thickness.
 5. The lamp of claim 1,wherein said phosphor layer has a thickness in the range of 5 to 500microns.
 6. The lamp of claim 1, wherein said air gap has a thickness inthe range of 5 to 1000 microns.
 7. The lamp of claim 1, furthercomprising a stepped reflector that forms a boundary for theencapsulation.
 8. The lamp of claim 7, wherein said stepped reflectorcomprises a wire bonding region.
 9. An illumination device comprising: apower source; a light emitting diode lamp in electrical communicationwith the power source, the light emitting diode lamp comprising: apackage; a least one light emitting diode; an encapsulation covering theat least one light emitting diode; a lens having a phosphor layer formedupon a bottom surface, wherein the lens is positioned to cover at leastpart of the encapsulation; and an air gap between the phosphor layer andthe encapsulation.
 10. The illumination device of claim 9, wherein saidphosphor layer comprises an inorganic dye.
 11. The illumination deviceof claim 9, wherein said phosphor layer has a uniform thickness.
 12. Theillumination device of claim 9, wherein said phosphor layer has avarying thickness.
 13. The illumination device of claim 9, wherein saidphosphor layer has a thickness in the range of 5 to 500 microns.
 14. Theillumination device of claim 9, wherein said air gap has a thickness inthe range of 5 to 1000 microns.
 15. The illumination device of claim 9,further comprising a stepped reflector that forms a boundary for theencapsulation.
 16. The illumination device of claim 15, wherein saidstepped reflector comprises a wire bonding region.
 17. A light emittingdiode apparatus comprising: a least one light emitting diode; anencapsulation covering the at least one light emitting diode; and a lenshaving a phosphor layer formed between first and second lens portions,the lens positioned so that the second lens portion fits against theencapsulation.
 18. The apparatus of claim 17, wherein said phosphorlayer comprises an inorganic dye.
 19. The apparatus of claim 17, whereinsaid phosphor layer has a uniform thickness.
 20. The apparatus of claim17, wherein said phosphor layer has a varying thickness.
 21. Theapparatus of claim 17, wherein said phosphor layer has a thickness inthe range of 5 to 500 microns.
 22. The apparatus of claim 17, furthercomprising a stepped reflector that forms a boundary for theencapsulation.
 23. The apparatus of claim 22, wherein said steppedreflector comprises a wire bonding region.